Chiral analysis of quenched baryon masses

Abstract

We extend to quenched QCD an earlier investigation of the chiral structure of the masses of the nucleon and the delta in lattice simulations of full QCD. Even after including the meson-loop self-energies which give rise to the leading and next-to-leading non-analytic behaviour (and hence the most rapid variation in the region of light quark mass), we find surprisingly little curvature in the quenched case. Replacing these meson-loop self-energies by the corresponding terms in full QCD yields a remarkable level of agreement with the results of the full QCD simulations. This comparison leads to a very good understanding of the origins of the mass splitting between these baryons.

Cutoff schemes in chiral perturbation theory and the quark mass expansion of the nucleon mass

“…We note that the terms beyond the O(p 3 ) truncation only contain even powers of m π , showing that the cutoff scheme employed here respects chiral symmetry at the one-loop level, since such terms are analytic in the quark masses and can thus be absorbed in the polynomial terms generated by the effective Lagrangian. We note that most of the regulating functions for one-loop diagrams proposed in [9] do not share this property, but generate e.g. terms ∼ m 5 π /Λ 2 χ , which can only be mapped onto a systematic chiral expansion at the two-loop level.…”

“…The authors of Refs. [9,10] therefore favored the use of a cutoff regularization scheme in their recent analysis of the nucleon mass, which in their eyes is more suitable for such a scenario. While the use of cutoff methods in CHPT already has a long history [11,12,7] and constitutes a well-defined regularization procedure, from the viewpoint of field theory it is not acceptable that one scheme should provide superior results over the other (for a general discussion of regularization schemes in CHPT, see e.g.…”

“…In that regime an effective field theory of QCD, usually called chiral perturbation theory (CHPT), can be set up, which is written in terms of the very Goldstone degrees of freedom, with their couplings to matter fields dictated by chiral dynamics [4,5,6]. Recently doubts have been issued in the literature [7,8,9,10] whether such an effective field theory, in particular when it is utilized in connection with dimensional regularization, is "effective" enough to be applied to extended objects with complicated internal structure like baryons. The authors of Refs.…”

Nucleons, nuclear matter and quark matter: a unified NJL approach

“…Calculations indicate it could be up to -400 MeV [36,37,38,39]. In the present work Σ N is varied by changing the dipole cut-off, Λ, within physically acceptable limits, in order to investigate how the pion cloud of the nucleon influences the equation of state of the system.…”

Decuplet baryon masses in partially quenched chiral perturbation theory

“…There has been much activity recently in calculating baryon properties in PQχPT [22,23,24,25,26,27,28,29,30,31,32,33]. There has also been interest in using chiral effective theories to extrapolate quenched and unquenched lattice data on the baryon masses, see for example [34,35,36].…”